import math  #include<math.h>

x1,y1,x2,y2 = map(float, input().split())
x = abs(x1 - x2)
y = abs(y1 - y2)

print(math.sqrt(x*x + y*y))

 import math math x1,y1,x2,y2 = map(float, input().split()) x1 map(float, input().split()) map float input().split() ().split () input split y1 x2 y2 x = abs(x1 - x2) x abs(x1 - x2) abs x1 - x2 x1 x2 y = abs(y1 - y2) y abs(y1 - y2) abs y1 - y2 y1 y2 print(math.sqrt(x*x + y*y)) print math.sqrt(x*x + y*y) math.sqrt math sqrt x*x + y*y x*x x x y*y y y y1,x2,y2 = map(float, input().split()) map(float, input().split()) y1 y2 = map(float, input().split()) map(float, input().split()) y2 y = abs(y1 - y2) abs(y1 - y2) y x2,y2 = map(float, input().split()) map(float, input().split()) x2 x = abs(x1 - x2) abs(x1 - x2) x x1,y1,x2,y2 = map(float, input().split()) map(float, input().split()) x1
import math  #include<math.h>

x1,y1,x2,y2 = map(float, input().split())
x = abs(x1 - x2)
y = abs(y1 - y2)

print(math.sqrt(x*x + y*y))


